Bolt mechanism for machine guns



Nov. 7, 1950 E. c. Hl-:DGl-:s 2,529,391

' BOLT MECHNISM FOR MACHINE GUNS mea Jan. s1, 194s @gli gy hisadministrar 72 Ei Wirf n Hayes z: horny Patented Nov. 7, 1950 BOLTMECHANISM FOR' MACHINE GUNS Ellsworth C. Hedges, deceased, late of WestHartford, Conn., by E. Warren Hedges, administrator, Manchester, Conn.,

assignor to Colts Manufacturing Company, a corporation of ConnecticutApplication January 31, 1946, Serial No. 644,502

Claims. 1

rIhe invention relates to a bolt mechanism for an automatic firearm ormachine gun of the Browning type and relates more particularly to a boltmechanism having the general characteristics of those disclosed inReissue Patent No. 19,159 to F. T. Moore et al., dated May 8, 1934, andin Patent N o. 1,936,254 to F. T. Moore, dated November 2l, 1933. Asdisclosed in the said patents, the longitudinally movable breech bolt isprovided at the top with pairsof grooves forming incomplete parts o twooppositely inclined intersecting cam paths, and is provided at theintersection of the cam paths with a recess in which is mounted anangularly movable cam block or switch The cam block has a groove thereinwhich is adapted to register with the grooves of either pair in the topof the bolt to complete either of the said cam paths. As shown in thesaid Patent No. 1,936,254, the angularly movable cam bloei; is providedwith a downward extending stem or pintle which its a bearing aperture inthe block and the said stem or pintle is provided with a circumferentialgroove into which projects the pivot stud of the extractor, the saidpivot stud thus serving to hold the cam block in place and to preventupward movement thereof without interfering with angular movement.

The construction shown in the said Patent No. 1,935,254 has been veryextensively used and has been found to be satisfactory, but it requiresvery close Yaccuracy of machining not only in the for* mation oi thegroove in the stem of the block but also in the size of the extractorstud and its bearing aperture and in the location of the stud bearingaperture with relation to the aperture for the stem of the block.Furthermore, the relatively deep pintle bearing aperture in the boltweakens the bolt, particularly in view of the fact that the said pintlebearing aperture necessarily intersects the horizontal bearing aperturefor the pivot stud of the extractor. aperture results in distortionduring manufacture and occasional breaking during use, particularly whenthe bolt has various cuts therein to reduce weight. The principal objectof the present invention is to provide a bolt mechanism wherein the camblock is held against vertical movement otherwise than by the extractorstud or by any other removable element engaging the stem or pintle ofthe cam block. With the improved construction the exact relativepositioning of the bearing aperture for the extractor stud islessimportant and there is less weakening of the bolt, and for these andother reasons desirable manufacturing economies are eiected and there isa reduced possibility of bolt breakage.

A further object of the invention is to make it possible for the camblock or switch to be more readily removed, it being unnecessary tofirst remove the extractor.

Other objects of the invention will be apparent This deep pintleY 2 fromthe following specification and claims and from the drawing.

ln the drawing there is shown in detail a preferred embodiment of theinvention, but it will bolt mechanism embodying the invention.

Fig. 2 is a view similar to Fig. 1 but showing the movable cam block ina different position.

Fig. 3 is a side view of the front portion of the bolt mechanism asshown in Fig. 2.

Fig. 4 is a view similar to Figs. l and 2 but showing the movable camblock in the position which it occupies during assembly and disassembly.

Fig. 5 is a fragmentary sectional view taken along the line 5 5 of Fig.1.

Fig. 6 is a fragmentary sectional view taken along the line 'ii-6 ofFig. 2.

Fig. 7 is an end view of the cam block.

Referring to the drawing, lil represents the longitudinally movablebreech bolt as an entirety, only the front portion thereof being shown.rIhe bolt is longitudinally reciprocable in the barrel extension of thegun and is guided therein by means which are the same as or similar tothose disclosed in Patent 1,936,254. The bolt Iii has a transversebearing aperture l2 therein for receiving the pivot stud of theextractor, which is not shown. The extractor is held in place by aflange thereon which enters an arcuate groove iii formed in the side ofthe bolt.

rilhe bolt is provided at the top with two pairs of grooves formingparts of two oppositely inclined intersecting cam paths, one of thesecam paths being adapted for use in feeding the cartridge belt from leftto right, and the other of them being adapted for use in feeding thecartridge belt from right to left. One of the cam paths comprises a pairof aligned grooves I and l formed in the top of the bolt and the otherof the cam paths comprises a pair of aligned grooves 2Q and 22 formed inthe top of the bolt. At the intersection of the cam paths, that is,between the grooves i6 and i and between the grooves 2li and '22, thebolt is provided with a recess 24 which is bounded by arcuate walls 2tand 28 conforming to a cylinder having a vertical axis at 33. The recess2t is located in part above the transverse bearing aperture i2 for thepivot stud of the extractor. Positioned within the recess 2li is anangularly movable cam block or "switch 32 which is shaped to fit orapproximately lit the walls 26 and 28. The cam block 32 has a groove 34in the top thereofl having the same cross sectional size and shape asthe grooves it, i3, 2Q and 22, and the cam block is angularly movable sothat the groove 34 can register with the grooves 2|] and 22 as shown inFig. l or with the grooves IS and IS as shown in Fig. 2. Thus the camblock 32 with its groove .34 serves to complete either of the cam pathsso as to adapt the bolt mechanism for feeding from left to right or forfeeding from right to left.

A releasable means is provided for holding the cam block in either ofthe positions last described, and as shown, this means comprises aspringpressed plunger 36 which can enter a hole 38 in the cam block tohold it in the position shown in Fig. l, or can enter a hole it in thecam block to hold it in the position shown in Fig. 2. When the cam blockis to be adjusted from one position to another the plunger 3S isdepressed by a Lsuitable tool.

In order to prevent relative upward movement of the cam block whilepermitting relative angular movement, the recess is provided withundercuts l2 and 44 which are below the said arcuate walls 25 and 28 andwhich extend radially outward therefrom, and the cam block is providedwith integral arcuate flanges it and 8 adapted to enter andapproximately rit the said underouts. It will be seen that with the camblock in either of the positions shown in Figs. l and 2 the entry of theflanges i6 and i3 in the undercuts [52 and ci@ eiectually prevents anyupward movement lof lthe cam block while leaving it free to moveangularly.

In order that the cam block may be engaged with or disengaged from thebolt, the two undercuts i2 and il!! are spaced apart. Preferably, therecess 2li has openings at its sides and the undercuts terminate at thesaid openings. When the block is moved to the position shown in Fig. 4,the flanges t6 and i3 are free from the undercuts and 44 and. are out ofvertical register therewith, and the block can be moved downward forassembly or upward for disassembly. The sides of the block 32 may belongitudinally grooved, as shown most clearly in Fig. 7, to facilitatehandling during assembly and disassembly. It will K be observed that itis not necessary to remove the extractor in order to engage or disengagethe block.

Preferably, the block is provided with a bearing aperture 553 which isconcentric with the axis 3S and the block 32 is provided with a stem orpintle which enters and closely fits the bearing aperture 5B. Thepintle'bearing aperture 55 is longitudinally spaced from the aperture i2for the pivot stud of the extractor, and the sides of the bearingaperture are preferably curved inwardly and downwardly as shown. Thesides of the pintle 52 are similarly curved inwardly and downwardly andthus the pintle has a large fillet at the top which serves to strengthenthe block, which would otherwise be relatively weak by reason of thedeep groove 3d therein, as shown in Fig?. The pintle may have a centralhole 5t therein to admit air to the space below the block, thusfacilitating removal thereof. The engagement ofthe pintle 52 with thebearing aperture 55 serves to center the block and to guide the angularmovement thereof thus making it unnecessary to provide a close fitbetween the periphery of the block and the periphery of the recess orbetween the peripheries of the anges and the peripheries of theundercuts. The fact that close fits'are not necessary is shown inexaggerated form in Fig. 5.

The bearing aperture 5@ is relatively shallow 4 in order to reduce to aminimum any weakening or" the bolt. As shown in Fig. 3, the bottom ofthe aperture is at a level above the bottom of the said transversebearing aperture I2. The shallow 'bearing aperture 5t and the shortpintle 52 are effective for guiding angular movement of the cam block byreason of the fact that the anges d6 and i8 in the undercuts l2 and lllprevent any upward movement of the block.

It will be seen that with the improved construction as shown anddescribed, the bearing aperture i2 for the extractor stud does notintersect the bearing aperture 5S for the pintle of the cam block, thusavoiding the weakening of the block which is necessarily incident tointersecting apertures. Furthermore, the aperture I2 can be positionedwith only such accuracy as is required for proper functioning of theextractor, and no consideration need be given to the exact relationshipbetween the two apertures. It is also evident that the pintle 52 isrelatively short and that the aperture 5i) for receiving it isrelarespectively tei ely shallow, thus additionally avoiding thevfeakening of the bolt which was incident to a deep aperture such asthat shown in Patent No. 1,936,254.

The manner o f useof the improved bolt mechanism as shown and describedis the same as disclosed in the said Patent 1,936,254 and reference maybe had to that patent for a description of the parts of the gun withwhich the bolt mechanism cooperates for a description of the functioningof the several parts.

What is claimed is:

l. A bolt mechanism for o machine gun comprising in combination, alongitudinally movable breech 1ooit provided at the top with a recesspartly bonne at its upper portion by longitudinally opposite arcuatewalls conforming to a cylinder` having a vertical axis which recess hasundercuts below the said arcuate walls and extending radially outwardtherefrom, the said bolt being also provided at the top with fourgrooves arranged in pairs to form incomplete parts of two oppositelyinclined intersecting cam paths with the adjacent ends of the grooves ofeach pair at and interrupting the said opposite arcuate walls of therecess, a cam block angularly movable in the recess about the said axisand provided at the top with a groove adapted to register with the saidgrooves of either pair inthe top of the `colt to complete either of thesaid paths, the said `cam bloclr having opposite arcuate wallsapproximately fitting the said opposite arcuate walls of the recess andalso having opposite integral flanges below the said arcuate walls ofthe recess of the com block and projecting outward into the saidundercuts in the recess to prevent upward movement of the cam blockwhile permitting angular movement thereof about the said axis, andreleasable means for holding the cam block with the groove in the topthereof in register with the grooves of either pair in the top of thebolt.

2. A bolt mechanism for a machine gun comprising in combination, alongitudinally movable breech bolt provided at the top with a recesspartly bounded at its upper portion by longitudinally opposite arcuatewalls conforming to a cylinder having avertical axis which recess hasundercuts below the said arcuate walls and extending radially outwardtherefrom and which recess includes a downward extending shallow bearingaperture concentric with the said aXis, the said bolt being alsoprovided at the top with four grooves arranged in pairs to formincomplete parts of two oppositely inclined intersecting cam paths withthe adjacent ends of the grooves 0f each pair respectively terminatingat and interrupting the said opposite arcuate walls of the recess, a camblock angularly movable in the recess about the said axis and providedat the top with a groove adapted to register with the said grooves ofeither pair in the top of the bolt to complete either of the said campaths, the said cam block having a short integral downward extendingpintle fitting the bearing aperture in the recess for guiding angularmovement of the block about the said axis and the said cam block havingopposite integral flanges below the said arcuate walls of the recess andprojecting outward into the said undercuts in the recess to preventupward movement of the cam block while permitting the said angularmovement thereof, and releasable means for holding the cam block withthe groove in the top thereof in register with the grooves of eitherpair in the top of the bolt.

3. A bolt mechanism for a machine gun comprising in combination, alongitudinally movable breech bolt provided at the top with a recesspartly bounded at its upper portion by longitudinally opposite arcuateWalls conforming to a cylinder having a vertical axis which recess hasundercuts below the said arcuate walls and extending radially outwardtherefrom and which recess includes a downward extending shallow bearingaperture concentric with the said axis and having its side walls curvedinwardly and downwardly, the said bolt being also provided at the topwith four grooves arranged in pairs to form incomplete parts of twooppositely inclined intersecting cam paths with the adjacent ends of thegrooves of each pair respectively terminating at and interrupting thesaid opposite 'arcuate walls of the recess, a cam block angularlymovable in the recess about the said axis and provided at the top with agroove adapted to register with the said grooves of either pair in thetop of the bolt to complete either of the said cam paths, the said camblock having a short integral downward extending pintle tting thebearing aperture in the recess for guiding angular movementfof the blockabout the said axis andthe said cam block having opposite integralflanges below the said arcuate walls of the recess and projectingoutward into the said undercuts in the recess to prevent upward movementof the cam block while permitting the said angular movement thereofabout the said axis, and releasable means for holding the cam block withthe groove in the top thereof in register with the grooves of eitherpair in the top of the bolt.

4. A bolt mechanism for a machine gun comprising in combination, a,longitudinally movable breech bolt having a, transverse horizontalbearing aperture for an extractor Vpivot stud and provided at the topwith a recess located in part above the said aperture and partly boundedat its upper portion by longitudinally opposite arcuate walls conformingto a cylinder having a vertical axis which recess has undercuts belowthe said :arcuate walls and extending radially outward therefrom andwhich recess includes a shallow downward extending bearing apertureconcentric with the said axis and longitudinally spaced from the saidtransverse bearing aperture, the said bolt being also provided at thetop with four grooves arranged in pairs to form incomplete parts of twooppositely inclined intersecting 'cam paths with the adjacent ends ofthe grooves of each pair respectively terminating at and interruptingthe said opposite arcuate walls of the recess, a cam block angularlymovable in the recess about the said axis and provided at the top with agroove adapted to register with the said grooves of either pair in thetop of the bolt to complete either of the said cam paths, the said camblock having a short integral downward extending pintle fitting thebearing aperture in the recess for guiding angular movement of the blockabout the said aXis and the said cam block having opposite arcuate wallsapproximately fitting the said opposite arcuate walls of the recess andalso having integral flanges below the said arcuate walls of the recessand of the cam block and projecting outward into the said undercuts inthe recess to prevent upward movement of the cam block while permittingthe said angular movement thereof, and releasable means for holding thecam block with the groove in the top thereof in register with thegrooves of either pair in the top of the bolt.

5. A bolt mechanism for a machine gun comprising in combination, alongitudinally movable breech bolt provided at the top with a recesshaving openings at its sides and bounded at its upper portion betweenthe said openings by longitudinally opposite arcuate walls conforming toa cylinder having a vertical axis which recess has undercuts below thesaid arcuate walls and extending radially outward therefrom, the saidbolt being also provided at the top with four grooves arranged in pairsto form incomplete parts of two oppositely inclined intersecting campaths with the adjacent ends of the grooves of each pair respectivelyterminating at and interrupting the said opposite arcuate walls of therecess, a cam block angularly movable in the recess about the said axisand provided at the top with a groove adapted to register with the saidgrooves of either pair in the top of the bolt to complete either of thesaid cam paths, the said cam block having arcuate walls at its said endsapproximately fitting the said opposite arcuate walls of the recess andalso having integral fianges at its ends below the said arcuate walls ofthe recess and of the cam block and projecting outward into the saidundercuts in the recess to prevent upward movement of the cam blockwhile permitting angular movement thereof and the said cam block beingnarrower at its ends than the respective openings in the sides of therecess so that it is engageable with or separable from the bolt byrelative vertical movement when the ends of the block are in registerrespectively with the said openings, and releasable means for holdingthe cam block with the groove in the top thereof in register with thegrooves of either pair in the top of the bolt.

E. WARREN I-IEDGE'S,

Administrator of the Estate of Ellsworth C'.

Hedges, Deceased.

REFERENCES CITED The following references are of record in the i'lle ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 19,159 Moore et al May 8,1934 1,369,646 Fuller Feb. 22, 1921 1,534,131 McBride Apr. 21, 19251,596,367 Miller Aug, 17, 1926 1,803,351 Moore et al May 5, 19311,920,984 Howard Aug. 8, 1938 1,936,254 Mooreret al Nov. 21, 1933'1,956,574 Hatcher um May l, 193%

